1. Technology Field
The present invention generally relates to implantable medical devices and delivery systems for implantable medical devices used in intravascular systems. In particular, the present invention relates to implantable medical device that are shaped and configured for placement within a bifurcated lumen of a human or animal.
2. The Related Technology
Stents, grafts, and a variety of other implantable medical devices or prostheses used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such implantable medical devices can be delivered and used in virtually any accessible body lumen of a human or animal, and can be deployed by any of a variety of recognized means. One recognized use of an implantable medical device, such as a stent, is the treatment of atherosclerotic stenosis in blood vessels. For example, after a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure a stent is often deployed at the treatment site to improve the results of the medical procedure and reduce the likelihood of restenosis. The stent is configured to scaffold or support the treated blood vessel; if desired, it can also be loaded with a beneficial agent so as to act as a delivery platform to reduce restenosis or the like.
Conventional implantable medical devices are typically designed to treat or repair lumens of a vessel or other tubular organ that are removed from bifurcations. It is often necessary, however, to repair or treat the lumen of a vessel or other tubular organ at or near a point of bifurcation. Using conventional implantable medical devices to treat lumen bifurcations presents various drawbacks and can be challenging. For example, due to the generally, straight tubular design of conventional implantable medical devices, several implantable medical devices are typically required to completely cover a bifurcated lumen. The use of multiple implantable medical devices can significantly increase the complexity of implanting the implantable medical devices, can result in the overlapping of implantable medical devices, and can nonetheless lead to inadequate scaffolding due to gaps between endoprostheses.
The use of a single conventional implantable medical device to treat a bifurcated lumen can also present various difficulties. For example, it is common to implant the proximal end of a conventional endoprosthesis within the main lumen of a bifurcated lumen and extend the distal end of the endoprosthesis into one of the lumen side branches. This type of placement may compromise the patency of the bifurcation by jailing off the other lumen side branch. So called “endoprosthesis jails” can restrict blood flow into, and prevent future treatment of, the distal portion of the jailed lumen branch.
Furthermore, when the bifurcated lumen is an artery or other vessel being treated due to atheroma, plaque can easily be shifted from the treated main lumen to the non-treated lumen branches, thereby occluding one or both of the lumen side branches. This is known as the “snowplow” effect. In addition to occluding one or both of the lumen branches, a dislodged atheroma can be swept downstream into one of the lumen side branches, which can pose high threats to patient safety. Other complications that may arise when using conventional endoprostheses to treat bifurcated lumens include vessel spasm, thrombosis, and embolism.
One reason conventional endoprostheses are typically inadequate for treating bifurcated lumens is that they do not account for the variation in lumen size that can occur at or near the bifurcation of a lumen. For instance, it is common for the diameter of the main lumen to increase near the ostium of the lumen side branches. Furthermore, depending upon the location of the bifurcated lumen, the size of the main lumen may vary along its length.
For example, at the left main region of a patient's anatomy, the left main vessel extends from the aorta and bifurcates into the left circumflex vessel and the crucial left anterior descending vessel. Due to the proximity of the left main vessel to the aorta, the size of the left main vessel can be quite large and vary along its length. The inability of conventional endoprostheses to compensate for variation in vessel size often means that the endoprostheses are either oversized or undersized, both of which can lead to severe complications. In particular, an endoprosthesis that is undersized may cause thrombus formation, whereas an endoprosthesis that is oversized may result in vessel rupture.
Additionally, conventional endoprostheses typically do not account for varying lesion characteristics that may be particular to a bifurcated is common for a lesion to build along lateral edges of the ostium in a circumferential manner, but not to form on the carina of the bifurcation (as used herein the term “carina” refers to the apex of a lumen bifurcation where the side branches split off from the main lumen). When treating such a lesion with conventional endoprostheses, the carina is often nonetheless contacted and supported by the endoprosthesis. In such cases, however, it may not be necessary or desirable to contact the carina. For example, contacting the carina can cause restenosis at the carina or otherwise damage the carina.